The invention relates to a mounting for the pulley discs of a belt-type cone pulley transmission in which two pulley discs are rotatably and axially displaceably arranged on a shaft. The pulley discs are coupled to one another in such a manner that they are axially movable with respect to one another, but are constrained to rotate in unison with respect to the shaft. Further, between the shaft, a support disc axially immobilized on the shaft and one pulley disc there is provided a mounting which takes up the radial and axial forces. At least the axial mounting is an anti-friction bearing having rolling surfaces extending substantially radially of the shaft, and further, the pulley discs are coupled with the shaft through a pressing device which operates dependent upon the torque or upon the torque and the transmission ratio.
Mountings of the above-outlined type are known and are disclosed, for example, in German Pat. Nos. 1,124,779 and 1,550,912 to which there correspond, respectively, U.S. Pat. Nos. 3,034,367 and 3,429,193. In these structures, however, the axial mounting is problematical, which, similarly to the radial mounting, is necessary only because upon a variation of the transmission ratio or upon a variation of the power to be transmitted by the transmission, the position of the cone pulley in relation to its shaft varies in the peripheral direction. This is so, because the mutually opposite cam paths of the pressing device vary their mutual relative position to adapt to the new working conditions. These difficulties stem from the fact that the axial bearings are also subjected, when the transmission is in rotation, to a rotating load. This is of particular significance because, on the one hand, the bearings are stationary during most of the operational periods since the transmission rotates with predetermined load and fixed ratio, and, on the other hand, because as a result of the rotating flexure of the pulley discs and shaft occurring due to the rotating load, only a small part of the axial bearing is ever in effective contact.
These circumstances cause a fretting corrosion and eventually result in the rolling bodies working themselves into the bearing surfaces, which could not be prevented hitherto even by special design measures such as additional lubrication or forced circulation of the rolling bodies.
According to German Pat. No. 1,550,912 an attempt was made to provide a remedy in that at least the fixed pulley discs are mounted on the transmission shaft merely by means of two bearings and that at least one of the bearings is formed as an oblique bearing to take up axial and radial forces, thus rendering possible a play-free support of the pulley disc on the shaft. It was found in practice, however, that even this arrangement does not entirely eliminate the described disadvantages.
A solution to the stated problem which is satisfactory for most cases has become known from German Pat. No. 2,016,181, to which there corresponds U.S. Pat. No. 3,722,308. Its object is based on the recognition that a wobbling movement occurs due to the superimposition of tilting movement and rotation of the respective pulley disc, caused by the rotating load. This wobble results, especially in the axial bearings which are designed only for a rolling movement in the peripheral direction, in small sliding movements between rolling bodies and bearing surfaces. This applies not only to rolling bodies in the form of cylinders but also to those in the form of balls, since their radial mobility is hindered by the bearing channel and its abutment shoulders. Once the rolling bodies have worked themselves into the bearing surfaces, a variation of transmission ratio of the transmission is only conditionally possible if at all, since, as a result of the detent effect between pulley discs and shaft, generated in the axial bearings, the necessary angular travel between pulley discs and shafts can no longer be executed or, at best, leads to a jolting and thus sudden variation of the transmission ratio.
Based on this recognition, according to German Pat. No. 2,016,181 the axial bearing is essentially of such configuration that, in case of flat rolling surfaces, the rolling bodies are formed as rotationally symmetrical ellipsoids cut away on both sides, or, in case convex bearing surfaces are provided, the rolling bodies are also formed as cylinders. Further, the rolling bodies are rotatably mounted in a retaining ring with a journal extending radially outwardy of the transmission shaft. Thus, an articulation effect of the axial mounting occurs, so that movement deriving from the corresponding wobbling movement of the associated pulley disc is converted into a rolling movement between rolling bodies and bearing surfaces.
In some instances where belt-type cone pulley transmissions are used, however, both axial and torsional oscillations occur on the axial bearing. The axial oscillations derive from the already-mentioned, rotation-caused flexure of pulley discs and shafts. the torsional oscillations are, however, introduced into the transmission from the exterior. The source of such torsional oscillations, for example, may be a jointed shaft which is coupled to the transmission and which generates an irregular peripheral speed at the cone pulley assembly. Such axial and torsional oscillations which frequently also occur with different amplitudes of oscillation, generate an increased slip within the axial bearing, thus damaging the balls, rollers or rolling surfaces, thereby preventing satisfactory operation of the transmission.